In marine bacteria and some thraustochytrids (marine stramenopiles) long-chain polyunsaturated fatty acids (LC-PUFAs) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are produced de novo by PUFA synthases. These large, multi-domain enzymes carry out the multitude of individual reactions required for conversion of malonyl-CoA to the final LC-PUFA products. Here we report on the release of fatty acids from the PUFA synthase found in Schizochytrium, a thraustochytrid that has been developed as a commercial source for DHA-enriched biomass and oil. Data from in vitro activity assays indicate that the PUFAs are released from the enzyme as free fatty acids (FFAs). Addition of ATP and Mg2+ to in vitro assays facilitates appearance of radiolabel from 14C-malonyl-CoA in a triacylglycerol fraction, suggesting the involvement of acyl-CoA synthetases (ACS). Furthermore, addition of triascin C, an inhibitor of ACSs, to the assays blocks this conversion. When the Schizochytrium PUFA synthase is expressed in Escherichia coli, the products of the enzyme accumulate as FFAs, suggesting that the thioesterase activity required for fatty acid release is an integral part of the PUFA synthase.

Polyunsaturated fatty acids (PUFAs) are essential membrane components in higher eukaryotes and are the precursors of many lipid-derived signaling molecules. Here, pathways for PUFA synthesis are described that do not require desaturation and elongation of saturated fatty acids. These pathways are catalyzed by polyketide synthases (PKSs) that are distinct from previously recognized PKSs in both structure and mechanism. Generation of cis double bonds probably involves position-specific isomerases; such enzymes might be useful in the production of new families of antibiotics. It is likely that PUFA synthesis in cold marine ecosystems is accomplished in part by these PKS enzymes.

Journal of PhycologyVolume 36, Issue 2 p. 259-260 More tools for diatom molecular biology research Paul G. Roessler, Paul G. Roessler Kelco BiopolymersSan Diego, California 92123e-mail: [email protected]Search for more papers by this author Paul G. Roessler, Paul G. Roessler Kelco BiopolymersSan Diego, California 92123e-mail: [email protected]Search for more papers by this author First published: 25 December 2001 https://doi.org/10.1046/j.1529-8817.2000.00ag2.xCitations: 4Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article.Citing Literature Volume36, Issue2April 2000Pages 259-260 RelatedInformation

The Aquatic Species Program was a relatively small research effort intended to look at the use of aquatic plants as sources of energy. Its history dates back to 1978, but much of the research from 1978 to 1982 focused on using algae to produce hydrogen. The program switched emphasis to other transportation fuels, particularly biodiesel, beginning in the early 1980's. This report summarizes the research activities carried out from 1980 to 1996, with an emphasis on algae for biodiesel production.

Photosynthetic performance of an eicosapentaenoic acid (EPA; 20:5ω3) deficient mutant of the eustigmatophyte Nannochloropsis sp. was compared to the wild type (Wt) strain in order to evaluate the effect of fatty acid composition on the function of the photosynthetic apparatus. Cellular photosynthetic capacity and the cellular pool of pigments and of reaction centers were reduced in the mutant concomitant with a reduction in the amount of thylakoid membranes and their volume-specific density. Despite the changes observed in photosynthetic activity, the fluorescence properties of the mutant were virtually the same as those of the wild type, although the phase transition of thylakoid membrane was recorded at higher temperature in the mutant than in the Wt. The results suggest that the change in one double bond in a very long chain fatty acid of the thylakoid lipids plays a minor role in regulating photosynthetic electron transport, but that the mutation modified the ability of the mutant to acclimate to low-irradiance conditions.

Genetic transformation of two species of diatoms has been accomplished by introducing chimeric plasmid vectors containing a bacterial antibiotic resistance gene driven by regulatory sequences from the acetyl-CoA carboxylase (ACCase) gene from the diatom Cyclotella cryptica. The recombinant DNA integrated into one or more random sites within the algal genome and the foreign protein was produced by the algal transformants. This is the first report of genetic transformation of any chlorophyll c-containing microalgal strain. We are using this system to introduce additional copies of the ACCase gene into diatoms in an attempt to manipulate lipid accumulation in transformed strains.